Field of the Invention
The present invention relates to an ink jet recording head and, more particularly, to an ink jet recording head capable of controlling the movement of colored particles in a pigmented ink by an electrophoretic force.
Non-impact recording methods attract a large attention in a-printing technology for their low noise during a recording operation. Among other non-impact recording methods, an ink jet recording method has several advantages of direct and high-speed printing onto a recording medium such as a plain paper. A variety of proposals are presented heretofore for improving the ink jet recording head.
A conventional ink jet recording head, such as described in JP-A-60(1985)-228162, comprises a plurality of ejecting electrodes and a counter electrode disposed behind a recording paper. A driving voltage is applied between a specified ejecting electrode and the counter electrode to generate an electric field, which applies an electrostatic force for ejecting colored particles in a pigmented ink from the ejecting electrode.
FIG. 1 shows a conventional ink jet recording head of the type as described above. The ink jet recording head comprises an ink chamber 301 having an ink jet slit 302 for ejecting therefrom colored particles in pigmented ink 310, an electrophoretic electrode 303 disposed at a rear wall of the ink chamber 301 for concentrating colored particles in the pigmented ink in the vicinity of the ink jet slit 302, a plurality of elongate, ejecting electrodes 305 arranged in a row along the ink jet slit 302 for ejecting ink droplets 311 of the colored particles from a specified ejecting electrode 305, and a counter electrode 309 disposed behind a recording medium or paper 304 for generating an electric field between the specified ejecting electrode 305 and the counter electrode 309.
Ink jet slit 302 is separated by separating walls 308 into a plurality of short channels each corresponding to one of the ejecting electrodes 305, thereby forming a meniscus of the pigmented ink 310 at each ejecting electrode 305. The ink chamber 301 is communicated to an ink reservoir not shown in the drawing by tubes connected to the ink inlet port 306 and an ink outlet port 307 for circulating the pigmented ink 310 by a back pressure applied to the pigmented ink in the ink chamber 301.
FIG. 2 shows voltage waveforms applied to the electrophoretic electrode and the ejecting electrodes of FIG. 1. The ink jet recording head utilizes an electrophoretic force by which the charged or electrified colored particles in the pigmented ink are moved in a specified direction.
Specifically, an electric field is generated in the ink chamber 301, which is filled with the pigmented ink, by applying a constant electrophoretic voltage V1, as shown in FIG. 2, to the electrophoretic electrode 303. The colored particles in the pigmented ink are moved by the electric field toward the ink jet slit 302 at a constant electrophoretic mobility and concentrated therein, thereby forming an ink meniscus at the front tip of each ejecting electrode 305. After the ejecting electrode 305 specified for ink ejection receives a voltage pulse having an amplitude of V2 and a duration of T2, the colored particles are further moved toward and concentrated at the tip of the specified ejecting electrode 305.
The colored particles overcomes the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force and are ejected from the tip of the specified ejecting electrode 305, forming minute ink droplets 311, in accordance with the timing in synchrony with the voltage pulse, to adhere to the recording medium 304. The operation described above is repeated until a desired image is formed on the recording medium 304.